Technical Abstract:
While the mammary fat pad appears responsive to nutrient partitioning hormone concentrations that change in response to an elevated plane of nutrition, the mammary parenchyma does not. Plane of nutrition has no influence on long-term mammary epithelial cell proliferation or parenchyma DNA accretion rates. Instead the time between birth and slaughter appears to have a substantial influence on prepubertal mammary development. Historically, experiments evaluating the effect of elevated nutrient intake on prepubertal mammary development have evaluated mammary development at puberty. Since body weight at puberty is typically not affected by plane of nutrition, assessment of mammary development has been done at a common body weight but substantially different ages. Our data demonstrates that it is this effect of nutrient intake on age at a common body weight that most greatly influences prepubertal mammary development. We postulate that the single most important variable affecting total parenchyma DNA is the length of time between birth and a given body weight and that the plane of nutrition affects the time necessary to reach this given body weight but has no direct influence on local or systemic control over the rate of parenchyma DNA accretion, mammary epithelial cell proliferation, or ultimately total parenchyma DNA.